The invention concerns a hydraulic valve system with a supply connection arrangement having a high-pressure connection and a low-pressure connection, a working connection arrangement, having two working connections connectable with a motor, with a directional valve, which is arranged between the supply connection arrangement and the working connection arrangement, and with a compensation valve, which is acted upon in a first operation direction by a spring and a pressure in a pressure chamber, which is connected with a load-sensing line, and in a second operation direction, which is opposite to the first operation direction, by a pressure at the directional valve.
A valve system of this kind is known from, for example, DE 199 19 015 A1.
A valve system of this kind is required for controlling a motor. In a hydraulically controlled working machine, such a motor is, for example, able to lift or lower a load. Such a valve system is particularly suited for controlling the hydraulic piston-cylinder systems of a backhoe, said systems being required to align or lower a backhoe arm, or to change the inclination of the arm, on which the bucket is fixed, in relation to the backhoe arm.
By means of the directional valve, the direction of the hydraulic fluid is controlled, in such a way that from the high-pressure connection it reaches one working connection or the other working connection. The compensation valve serves the purpose of maintaining the pressure difference over the directional valve as constant as possible.
Problematic with such a valve system are cases, in which the motor that is supplied with hydraulic fluid via the working connections, is driven from the outside, for example when having to lower a load, or when the motor swings a backhoe uppercarriage with boom. Particularly in the latter case, the high mass inertia may cause the motor to require more fluid than the valve system can provide. The proportional valve is set at a certain flow value, for example 40 liters. The load to be moved is then strongly pushed and starts moving, for example turning. Due to the mass inertia, it can have such a large swing that it travels ahead of the supplied fluid volume, that is, the sufficient amount of oil is no longer supplied. Eventually, the mass gets slower, and has a driving effect, that is, the motor acts as a pump. After a certain time, the mass is slow enough, so that the fluid is again sufficient, and drives the motor. This causes oscillations. Such an oscillation inclination is undesirable.